1. Field of the Invention
The invention relates to closure caps for containers and, more particularly, to a reusable closure cap for containers having multiple sealing zones and a frangible locking means which can visually indicate whether the container has been opened.
2. Description of the Prior Art
Closure caps having a tamperproof feature have become an important item of commerce. Generally speaking, closure caps of this class include a locking member of some kind which interacts with a locking member included as part of a container. Upon breaking of the closure cap locking member, the cap can be removed from the container. Desirably, the closure cap locking member can be inspected visually to determine whether it has been tampered with. Accordingly, a consumer can readily detect whether the container has been opened previously.
Although container closures of this general class can function effectively, certain problems have not been addressed. One of these problems relates to reusability of the closure cap. With many closure caps made of a plastics material or metal foil, a so-called tear tab is pulled when it is desired to remove the closure cap from the container. Rupture zones often are provided in order to permit the tab to be torn easily. Sometimes the tab tears completely through the side wall of the cap and into the top wall of the cap. When this occurs, either by design or by accident, it is easy to remove the cap from the container, but the cap cannot be reused to seal the container again.
In an attempt to avoid the foregoing problem, container closure caps having tear tabs which do not enter the top wall of the cap have been provided. Certain of these caps are not reusable because, during the opening process, a skirt portion of the cap is sufficiently weakened that a good sealing function no longer can be carried out. Other caps are known in which a small locking member in the skirt portion of the cap is broken, either to permit removal of the cap or upon removal of the cap, but these caps also suffer certain drawbacks with respect to sealing capabilities.
Particularly when sealing a container containing a substance such as milk, it is quite important that the sanitary condition of the milk be maintained. In addition to at least one primary sealing area, it is desirable to provide a so-called bug shield in order to prevent dust, dirt, small insects, and so forth from having access even to the primary sealing area. Known container closures for milk containers either do not have a bug shield or are expensive to manufacture. Desirably, a closure cap for a milk container would be inexpensive to manufacture, easy to detect whether it had been opened previously, would adequately shield the primary sealing area from contamination, and would have desirable qualties of appearance.
Other types of containers are best sealed by a threaded closure cap. Prior threaded closure caps having tear tabs have not performed particularly well and tear tabs generally have been avoided with threaded caps. One known threaded closure cap not employing a tear tab is usable repeatedly, but it is made of relatively thick metal and it is difficult to initially untwist the cap from the container. In another known closure cap made of a plastics material, a so-called tear ring is disposed about the lower periphery of the cap. The tear ring includes serrations which engage mating serrations formed on the outer surface of the container. When it is desired to remove the cap, the tear ring is ripped from the cap and thrown away. Thereafter, the cap can be unthreaded because the mating serrations no longer prevent removal of the cap.
A problem with the foregoing construction is that it sometimes is difficult to grasp the tear ring in order to expeditiously remove it. Moreover, it is difficult to manufacture the cap such that the tear ring is connected to the remainder of the cap with material of the proper thickness. That is, a circumferential line of weakness between the tear ring and the remainder of the cap must be provided, and it is difficult to form such a line of weakness in a molding operation without ripping the tear ring from the closure cap upon removal of the cap from the mold.